This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 2000-012269 filed in Japan on Jan. 20, 2000; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a device for generating a plasma, in the manufacturing process of semiconductor devices or liquid crystal displays, or in any other microelectronic process, which is used for performing various processes such as, for example, etching, ashing, deposition, surface modification, and surface cleaning.
The present invention also relates to a plasma processing apparatus comprising such a device.
This application is based on Japanese Patent Application No. 2000-12269, the contents of which are incorporated herein by reference.
2. State of the Related Art
In the manufacturing process of semiconductor devices or liquid crystal displays, or in any other microelectronic process, a variety of plasma processes are widely used in order to perform various processes such as, for example, etching, ashing, deposition, surface modification, and surface cleaning. Such a plasma process includes steps of generating a plasma in a vacuum and applying the plasma to a substrate.
For generating a plasma discharge, various principles are known to those skilled in the art. Particularly, it is well known to generate a plasma by using a radiant field from a slot antenna in a microwave band. This plasma generating method has an advantage that it can very easily generate a plasma at high density. In particular, a plasma discharge generated by a slot antenna using an alternating electromagnetic field in the microwave band is now attracting attention, since it has a large uniformity in plasma density distribution because its generating principle is based on a surface wave excitation.
In this case, as shown in FIG. 1A, even if a plasma distribution at a plasma generating area is uniform, it will become non-uniform at the neighborhood of a wafer located under the generating area due to lateral diffusion of constituting species of the plasma.
Therefore, in order to obtain a uniform plasma distribution at the neighborhood of the wafer, as shown in FIG. 1B, it is required that a plasma distribution at the plasma generating area be a so-called xe2x80x9craised-shoulderxe2x80x9d shape, that is, the shape in which the plasma density at each edge portion is larger than that at a central portion.
Thus, in the case of a plasma generation using slot antennas, when it is desired to obtain the raised-shoulder shape plasma distribution above, one may locate slot antennas at a distribution corresponding to the desired distribution of the plasma density. That is, one may try to control the initial plasma distribution by setting the distribution of slot antennas.
In principle, slot antennas are located at any distribution. But, practically, the positioning of slot antennas is restricted due to the following reason:
Even if a slot antenna were located where the amplitude of a microwave propagating within a wave guide is small, the strength of the electromagnetic field radiated from the slot antenna will be weak. On the contrary, from a slot antenna located where the amplitude of a microwave is large, a strong electromagnetic field will be radiated. Therefore, in order to obtain a high density plasma by maximizing the plasma generation efficiency, a slot antenna must be located where the amplitude of a microwave is relatively large. Typically, in the case of a standing wave, the highest amplitude spots are regularly and discretely formed at intervals of half of the wavelength. Slot antennas can then be located at only such highest amplitude spots. Thus, it is practically impossible to control the initial distribution of a plasma by designing the distribution of slot antennas.
Taking the above circumstances into consideration, it is one object of the present invention to provide a plasma generating device in which the degree of freedom to position slot antennas is increased, while the initial plasma distribution, i.e. the plasma distribution in the area where the plasma is just generated, can be controlled as desired.
It is another object of the present invention to provide a plasma processing apparatus comprising such a plasma generating device.
To this end, the present invention proposes a plasma generating device comprising a wave guide for propagation of a microwave from a microwave oscillating source; a radiative part being connected to the wave guide for receiving the microwave therefrom and having slot antennas, each of the slot antennas being adapted to radiate electromagnetic radiation corresponding to the microwave existing at respective locations of slot antennas; and a plasma generation chamber being connected to the radiative part via a window made of a dielectric material and being adapted to receive the electromagnetic radiation from the slot antennas; wherein one or more dimensions of the radiative part is/are locally modified or is/are locally changeable, so that the actual wavelength within the radiative part is allowed to be locally changed, thereby the amplitude distribution of the electromagnetic radiation being radiated from the slot antennas towards the plasma generation chamber can be controlled.
Preferably, the frequency of the microwave may be in the range of between 1 GHz and 50 GHz.
Preferably, each slot antenna defines a slot, and the total edge length of each slot may be substantially equal to the ideal wavelength of the microwave in free space.
Preferably, each slot may be disposed with its longitudinal direction being oriented at a right angle or at any angle other than a right angle with respect to the propagation direction of the microwave within the radiative part.
Preferably, either the height or the width of the radiative part may be changeable. Particularly, either the height or the width of the radiative part may be gradually changed. More particularly, the changing rate thereof may be changeable.
Preferably, the shape of the radiative part may be rectangular, and the width of the radiative part near the slot antennas may be changeable. Particularly, the width of the rectangular radiative part near the slot antennas may be gradually changed. More particularly, the changing rate thereof may be changeable.
Practically, a plunger made of an electrically conductive plate may be provided at the end of the radiative part so as to be slidable with respect to the propagation direction of the microwave within the radiative part. In use, the electric potential of the plunger may be maintained to be equal to the electric potential of the radiative part.
If desired, a plurality of radiative parts may be connected to the wave guide. In this case, preferably, a plurality of plungers is provided at each end of the plurality of radiative parts so as to be slidable with respect to the propagation direction of the microwave within the respective radiative part. In use, similarly, the electric potential of each plunger may be maintained to be equal to the electric potential of the respective radiative part.
The present invention also proposes a plasma processing apparatus, this apparatus is characterized by comprising the above plasma generating device.
Preferably, in the plasma processing apparatus, a support for an article to be processed may be provided in the plasma generating chamber with one surface of the support opposite to the window. AC voltage or DC voltage may be applied to the support.
Preferably, the support is provided with a mechanism for controlling the temperature of the article to be processed.
We will now explain the basic principle of the present invention.
The present invention is based on the fact that the actual wavelength within a wave guide varies depending on the dimensions of the wave guide. Assuming that the wave guide used is a rectangular wave guide as shown in FIG. 2A, the actual wavelength within this type of wave guide at the TE01 mode is given the following equation:   λg  =      λ                  [                  1          -                                    (                                                λ                  /                  2                                ⁢                a                            )                        2                          ]                    1        /        2            
wherein xcexg is the actual wavelength at which the wave propagates within the wave guide; xcex is the ideal wavelength at which the wave propagates in free space; and (a) is the width of the rectangular wave guide.
Thus, the actual wavelength xcexg varies as a function of the width (a) of the wave guide (see FIG. 2B).
As is easily understood, not only in the case of a rectangular type of wave guide, but also in the case of any shape wave guide, the actual wavelength can be altered by changing one or more local dimensions of the wave guide. By altering the actual wavelength as such, the position of the highest amplitude spots can be shifted as desired within the wave guide.
Therefore, the particularly preferable designing method according to the present invention has the steps of:
(i) determining the ideal initial plasma distribution (for example, the raised-shoulder shape plasma distribution as shown in FIG. 1B) which will cause uniform plasma distribution at the neighborhood of a wafer;
(ii) positioning slot antennas at the distribution corresponding to said initial plasma distribution determined above; and
(iii) locally and appropriately changing one or more dimensions of a wave guide (changing of one or more dimensions may be either variable type or non-variable type) around which slot antennas is to be located depending on said distribution of antennas.
Thus, the actual wavelength can be locally altered so that the positions of the highest amplitudes can be shifted to the positions at which slot antennas are located, thereby the desired initial plasma distribution is obtained. In this case, it is noted that high density plasma is obtained with maximized plasma generating efficiency.
Accordingly, in the present invention, irrespective of conventional restriction that slot antennas must be located at an interval of half of a wavelength, even if slot antennas are located at any distribution, each slot antenna is allowed to radiate electromagnetic waves with the substantially highest radiation efficiency. That is, in the present invention, a desired initial plasma distribution is obtained by optionally setting the distribution of slot antennas.
In the above, the description is made for allowing all slot antennas to radiate electromagnetic waves with the highest radiation efficiency. However, if desired, the radiation efficiency from specific slot antennas may be xe2x80x9cintentionallyxe2x80x9d reduced in order that the plasma distribution actually formed becomes as close as possible to the desired initial plasma distribution. The principal goal of the present invention is obtaining the initial plasma distribution which will cause uniform plasma distribution near the wafer, rather than maximizing the radiation efficiency from all slot antennas.